Agriculture Reference
In-Depth Information
8.5 t/ha, the saving would amount to 44 kg of N per ha. Since the expenses per kg N
for fertilizers - with the exception of anhydrous ammonium - are around 1 euro, the
monetary savings would add up to 44 euros per ha. Hence the financial value of the
eventual yield increase on the one hand or of the possible saving in nitrogen fertil-
izer instead of this on the other hand hardly differs and therefore is represented in
Fig.
9.41
by a common green line.
The benefits via higher yields or via lower expenses for nitrogen plus those via
the higher
capacity of the combine
cross the cost curve for the control technique
for an annually fertilized area of about 175 ha. So this area should be exceeded
for an economic investment. Since a fertilizer spreader or sprayer with a width of
20 m and a speed of 10 km/h theoretically covers 20 ha per hour, this area might
even be handled per day. With large farms or by means of contract management,
annual areas of 1,000 ha or more can easily be treated per machine set. Under
these circumstances, the financial advantage of site-specific application as repre-
sented by the difference between the sum of the benefits and the cost of the con-
trol technique (Fig.
9.41
) can go up to 40-50 euros per ha. This explains why in
practice site-speciic nitrogen application has become a leading technique in pre-
cision farming.
In addition, there may be benefits from better
qualities
of the harvested products
and from less
leaching of nitrogen
into ground-waters. Future experience will
show how these benefits should be evaluated. And more knowledge about the best
control algorithms will help to fully exploit the possibilities with various crops.
9.5
Summary
The prospects for the realization of
site-specific fertilization
concepts differ sub-
stantially among nutrients:
•
for phosphorus, the application according to a mapped removal by previous
crops is promising. An alternative to this might be the control of fertilizing via
flat surface-soil-sensing by visible and near-infrared reflectance.
•
as for potassium, too fertilizing proportional to the mapped removal by previous
crops has good prospects. However, contrary to phosphorus this holds not for
sandy soils.
•
concerning nitrogen, excellent prospects exist for sensing the supply and hence
the need during distributing via the reflectance of the crop. This limits the appli-
cation to the respective growing period. Yet this temporal limitation is inevitable
as long as efficient nitrogen fertilizing necessitates “immediate feeding” of the
crop.
•
for the control of soil pH via calcium or magnesium, sensing and mapping the
situation by means of ion-selective-electrodes is a promising technique.
With many applications, a site-specific control that takes into account several
soil- or crop properties simultaneously might be worth to aim at in the future.
